With the close of 2010 just weeks away, it’s a good time to reflect on the notable medical stories of the year. We can’t forget the historic passage of health care reform by Congress. Or the invasion of bed bugs from coast to coast. Or the spotlight shone on concussive injuries sustained in football and other contact sports.

What about the most important medical development of 2010? For this my vote goes to a study published online in Science on July 20, which found that 1% tenofovir gel used before and after sexual intercourse reduced the rate of new HIV infections in women by 39% and cut the rate of transmission of HSV-2 infections by 50% (Science doi: 10.1126/science.1193748). A full story about the study was reported by my colleague Mitchel L. Zoler from the 18th International AIDS Conference in Vienna, where the findings were unveiled.

More studies of tenofovir are needed, to be sure, but this was the first study to prove that 1% tenofovir gel can stop HIV transmission in its tracks. The clinical implications of the findings are significant, especially in sub-Saharan Africa, where an estimated 22.5 million adults and children live with AIDS.

“Is it good enough? No,” reproductive infectious diseases expert Sharon L. Hillier, Ph.D., said at this summer’s annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology in Santa Fe, N.M. “Do we need something that’s 80% effective? Absolutely. But I have to tell you: from working in the microbicide field for 15 years, this was a startling and wonderful finding. Many of us were not surprised by the results, but so thrilled that finally there was something that looked like it was working.”